A. Field of the Invention
The present invention relates to a thermal television camera tube operating in the near-infra-red or far-infra-red range.
B. Discussion of the Prior Art
A tube of this kind is equipped with a pyroelectric target or retina upon which the incident radiation creates a temperature profile, the latter creating an electrical bias profile within the thickness of the target and, consequently, an electrical charge profile which may be read out by an electron-beam scanning the target point by point. The electrical signals obtained during the course of this scanning operation, constitute the image of the object from whence the radiation comes. Tubes of this kind are known in the prior art; it is for this reason that no detailed discussion of the conditions under which they operate will be given, since these conditions are described in particular in U.S. patent application Ser. No. 243,210 (U.S. Pat. No. 3,774,043).
It should be pointed out that a pyroelectric target, for reasons of sensitivity, should be very thin; a thickness in the order of some few tens of microns is normally employed. For example, with a material such as glycocoll sulphate, also known as triglycine sulphate (TGS) which is frequently employed in this kind of application, a frequently used thickness is 25 microns.
For reasons associated with the resolving power, a circular target is customarily employed typically having a diameter of at least 30 mm.
A target of this kind takes the form of a very thin, and therefore extremely fragile, component which must, as far as possible, be protected from the vibrations which it may experience in the tube in which it is mounted. This sensitivity to vibration, quite apart from the threat which it poses to the mechanical integrity of the target, also tends to cause an alteration in the output signal referred to as "microphoning."